The game was published by Activision for Microsoft Windows, PlayStation 3, and Xbox 360. Officially announced on February 11, 2009, the game was released worldwide on November 10, 2009. It is the direct sequel to Call of Duty 4: Modern Warfare, continuing along the same storyline and gameplay. It was released in conjunction with two other Call of Duty games: Call of Duty: Modern Warfare: Mobilized for the Nintendo DS, and Call of Duty: Modern Warfare: Reflex, a port of Call of Duty 4 adapted by Treyarch for the Wii console. In addition, a comic book series based on one of the game's characters was also produced, entitled Modern Warfare 2: Ghost.
Multiplayer is similar to the previous two titles on Xbox 360 and PlayStation 3. However, multiplayer on the PC is quite different from previous games. The PC version no longer includes dedicated server support. While previous Call of Duty titles allowed multiplayer matches with up to 64 people and user-made maps and mods, Modern Warfare 2 on PC is almost identical to console versions.
The ranking system works in the same way as the previous two games. As the player plays matches, they will gain XP. Once the player reaches a certain amount of XP, the player will level up. There are now a total of 70 levels in Modern Warfare 2, as opposed to 55 in Call of Duty 4: Modern Warfare and 65 in Call of Duty: World at War. There are also 10 levels of prestige, just like in the other two games. As in World at War, the player can unlock a total of 5 extra custom class slots by the 9th prestige.
Weapons attachments return in Call of Duty: Modern Warfare 2 with a few changes. Firstly, new attachments were introduced, such as the Thermal Scope and Heartbeat Sensor. Secondly, some weapon attachments are now unlocked through the use of other attachments, such as getting 20 kills looking through the ACOG Scope to unlock the Thermal Scope or 60 kills looking down the RDS to unlock the Holographic Sight. Lastly, the Grip and Grenade Launcher no longer count as a tier one perk. Enemies throughout the campaign will now carry weapons customized with a variety of attachments. When a player goes to pick up a weapon, it will actually tell them what attachments the gun has, except when the gun is using Bling or does not have any attachments.
